1. Field of the Invention
The present invention relates to a battery module provided with a structure for connecting a plurality of such battery modules arranged adjacent each other to constitute a battery pack, with which the plurality of battery modules can be precisely positioned with respect to each other.
2. Description of Related Art
A known battery pack is constructed with a plurality of sealed, flat prismatic battery modules coupled adjacent each other and connected in series. Each of the battery modules comprises a plurality of prismatic cell cases having short lateral walls 41 and long lateral walls 42, these being coupled together, sharing their short lateral walls, thereby constituting an integral battery case, shown in FIG. 7. When the short lateral walls 41 are shared they may also be referred to as xe2x80x9cpartition walls.xe2x80x9d Each cell case accommodates therein elements for electromotive force in a sealed condition. The plurality of battery modules are aligned adjacent and positioned with respect to each other by coupling locating projections and corresponding indentations provided on the long side faces of the battery modules. End plates are arranged on the opposite ends in the direction of arrangement of the battery modules, and the battery modules are coupled together by binding these end plates with restricting bands. In this state, electrode terminals arranged at opposite ends in the longitudinal direction of each battery module are connected with each other.
More specifically, referring to FIG. 6, the plurality of battery modules 31 having their positive and negative electrode terminals (not shown) at opposite ends thereof are arranged such that electrode terminals of opposite polarities are arranged aligned alternately. The locating projections 32 and indentations 33 are provided on the long lateral walls of adjacent battery modules 31 so that they face each other. Thus, by fitting the locating projections 32 of one battery module into corresponding indentations 33 of adjacent battery module, the plurality of battery modules 31 can be positioned with respect to each other in their longitudinal direction, and the electrode terminals of both polarities (not shown) are aligned in one line, which are then connected with bus bar modules (not shown).
However, there was the following problem in the above connecting structure of the battery pack. That is, the locating projections 32 and indentations 33 are provided at positions corresponding to partition walls between the plurality of cells 34 that constitute the battery module 31, as shown in FIG. 7. As charging and discharging are repeated, expansion of electrode plates occurs within the cells or the internal pressure within the cells may rise, as a result of which the walls of the cells bulge as shown in the drawing while the partition walls of the cells remain the same. Therefore, if the walls of the cells 34 protrude to a height greater than that of the locating projections 32, the locating projections 32 may come off the indentations 33, whereupon the neighboring battery modules will be dislocated. If, under such state, the battery modules move due to vibration or acceleration acted thereon, the connecting portions between the electrode terminals and bus bars are subjected to a great load, risking damages to the mounting structure of the electrode terminals.
While the entire length of the group of battery modules 31 arranged adjacent each other in the direction of arrangement is restricted by the end plates and restricting bands, since expansion of cell cases as mentioned above occurs in some of the battery modules 31, it can happen that cell cases 34 of some battery modules 31 bulge out, pushing the cell cases of other battery modules.
In view of these problems of the prior art, it is an object of the present invention to provide an improved structure for connecting battery modules to construct a battery pack, wherein the positioning function of the battery modules is not compromised even when battery cases expand by repeated charging and discharging.
To achieve the above object, a battery module according to the present invention comprises:
a plurality of prismatic cell cases having short lateral walls and long lateral walls coupled together such that each of the short lateral walls of these cell cases is common to two adjacent cell cases, thereby constituting an integral battery case, and each of the cell cases respectively accommodating therein elements for electromotive force;
a positive electrode terminal and a negative electrode terminal arranged at lengthwise opposite ends of the integral battery case; and
a locating projection and an indentation formed substantially in the center of cell cases that are positioned symmetrical with respect to a centerline in the lengthwise direction of the integral battery case.
According to the present invention, even when the battery cases expand during charging and discharging, the locating projections do not come off the indentations since they are arranged on portions where the walls of the cell cases bulge out most. Therefore, the battery modules remain fixedly positioned with respect to each other, so that even if they are subjected to vibration or acceleration, the battery modules will not be displaced and there will be no risk that the mounting portions of the electrode terminals are damaged.
The diameter of the projection should preferably be smaller than the diameter of the indentation, so that the projection is received in the indentation loosely to permit expansion or contraction of the cell cases and to accommodate dimensional or positional tolerances.
The projection should preferably be formed in a tapered or hemispherical shape, so that, when the battery modules are roughly aligned adjacent each other, they can be positioned with respect to each other of their own accord. Assembling efficiency of the battery pack can thereby be improved.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.